1. Field of the Invention
The present invention relates to a dielectric resonant component, and more particularly to a dielectric resonant component in which a plurality of dielectric resonators are formed in a single dielectric block.
2. Description of the Related Art
FIG. 21 is an exploded perspective view showing the configuration of a conventional dielectric multistage resonator used in, for example, an automobile telephone or a portable telephone. In FIG. 21, three inner conductor formation holes 10a to 10c are formed between a first surface 1a and a second surface 1b of a dielectric block 1 made of ceramics or the like, in such a manner that the holes 10a to 10c pass through the dielectric block 1. On the inner surface of each of the inner conductor formation holes 10a to 10c, an inner conductor 11 is formed. A dielectric substrate 2 made of ceramics or the like is mounted on and fixed to the lower surface 1d of the dielectric block 1. After the dielectric substrate 2 is mounted on and fixed to the dielectric block 1, an outer conductor 12 is formed so as to cover the outer surface of the dielectric block 1 and that of the dielectric substrate 2. The outer conductor 12 is grounded. The inner conductor 11 in each of the inner conductor formation holes 10a to 10c has one end which is open with respect to (or isolated from) the outer conductor 12 formed on the first surface ia of the dielectric block 1, and the other end thereof is short-circuited to the outer conductor 12 formed on the second surface 1b of the dielectric block 1. On the right and left side surfaces of the dielectric substrate 2, a pair of input/output electrodes 22 are formed. Each of the input/output electrodes 22 extends onto the upper and lower surfaces of the dielectric substrate 2.
The above-mentioned conventional dielectric multistage resonator includes three dielectric coaxial resonators in a single dielectric block. By appropriately changing the coupling relationship between these dielectric coaxial resonators by means of external coupling elements (capacitors, coils, or the like), a high-frequency device such as a filter (a BEF, a BPF, an LPF, an HPF, or a polar BPF) is constructed.
As described above, a conventional dielectric multistage resonator is constructed by mounting the dielectric substrate 2 on the dielectric block 1. However, it is difficult to securely adhere the dielectrics together due to technical limitations, so that the outer conductor 12 easily cracks at the junction between the dielectric block 1 and the dielectric substrate 2. As a result, Q decreases. When cracks are caused in the outer conductor 12 on the second surface 1b of the dielectric block 1, Q significantly decreases.
In addition, between the dielectric block 1 and the dielectric substrate 2, no electrode is formed except for at the portions of the input/output electrodes 22. Accordingly, if the input/output electrodes 22 have various thicknesses, the gap between the dielectric block 1 and the dielectric substrate 2 may vary. This produces a problem in that the characteristics of the dielectric resonant component are greatly affected.
Furthermore, in a conventional dielectric multistage resonator, the size of the dielectric block 1 varies depending on the type of a product to which the resonator is applied, so that the interval between the input/output electrodes 22 is changed in accordance with the type of the product. Therefore, it is necessary for a user to change the design of a circuit board depending on the type of the dielectric multistage resonator to be employed. This is very troublesome and creates a problem.
Moreover, the coupling relationship between the dielectric resonators is conventionally changed by coupling elements which are disposed outside the dielectric multistage resonator, thereby causing the size and cost of the resonator to be increased.